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DNSSEC-TRUST-ANCHORS.D(5) dnssec-trust-anchors.d DNSSEC-TRUST-ANCHORS.D(5)

NAME
dnssec-trust-anchors.d, systemd.positive, systemd.negative - DNSSEC trust anchor
configuration files

SYNOPSIS
/etc/dnssec-trust-anchors.d/*.positive

/run/dnssec-trust-anchors.d/*.positive

/usr/lib/dnssec-trust-anchors.d/*.positive

/etc/dnssec-trust-anchors.d/*.negative

/run/dnssec-trust-anchors.d/*.negative

/usr/lib/dnssec-trust-anchors.d/*.negative

DESCRIPTION
The DNSSEC trust anchor configuration files define positive and negative trust anchors
systemd-resolved.service(8) bases DNSSEC integrity proofs on.

POSITIVE TRUST ANCHORS
Positive trust anchor configuration files contain DNSKEY and DS resource record definitions
to use as base for DNSSEC integrity proofs. See RFC 4035, Section 4.4[1] for more information
about DNSSEC trust anchors.

Positive trust anchors are read from files with the suffix .positive located in
/etc/dnssec-trust-anchors.d/, /run/dnssec-trust-anchors.d/ and
/usr/lib/dnssec-trust-anchors.d/. These directories are searched in the specified order, and
a trust anchor file of the same name in an earlier path overrides a trust anchor files in a
later path. To disable a trust anchor file shipped in /usr/lib/dnssec-trust-anchors.d/ it is
sufficient to provide an identically-named file in /etc/dnssec-trust-anchors.d/ or
/run/dnssec-trust-anchors.d/ that is either empty or a symlink to /dev/null ("masked").

Positive trust anchor files are simple text files resembling DNS zone files, as documented in
RFC 1035, Section 5[2]. One DS or DNSKEY resource record may be listed per line. Empty lines
and lines starting with "#" or ";" are ignored, which may be used for commenting. A
<consant>DS</consant> resource record is specified like in the following example:

. IN DS 19036 8 2 49aac11d7b6f6446702e54a1607371607a1a41855200fd2ce1cdde32f24e8fb5

The first word specifies the domain, use "." for the root domain. The domain may be
specified with or without trailing dot, which is considered equivalent. The second word must
be "IN" the third word "DS". The following words specify the key tag, signature algorithm,
digest algorithm, followed by the hex-encoded key fingerprint. See RFC 4034, Section 5[3] for
details about the precise syntax and meaning of these fields.

Alternatively, DNSKEY resource records may be used to define trust anchors, like in the
following example:

. IN DNSKEY 257 3 8 AwEAAagAIKlVZrpC6Ia7gEzahOR+9W29euxhJhVVLOyQbSEW0O8gcCjFFVQUTf6v58fLjwBd0YI0EzrAcQqBGCzh/RStIoO8g0NfnfL2MTJRkxoXbfDaUeVPQuYEhg37NZWAJQ9VnMVDxP/VHL496M/QZxkjf5/Efucp2gaDX6RS6CXpoY68LsvPVjR0ZSwzz1apAzvN9dlzEheX7ICJBBtuA6G3LQpzW5hOA2hzCTMjJPJ8LbqF6dsV6DoBQzgul0sGIcGOYl7OyQdXfZ57relSQageu+ipAdTTJ25AsRTAoub8ONGcLmqrAmRLKBP1dfwhYB4N7knNnulqQxA+Uk1ihz0=

The first word specifies the domain again, the second word must be "IN", followed by
"DNSKEY". The subsequent words encode the DNSKEY flags, protocol and algorithm fields,
followed by the key data encoded in Base64. See RFC 4034, Section 2[4] for details about the
precise syntax and meaning of these fields.

If multiple DS or DNSKEY records are defined for the same domain (possibly even in different
trust anchor files), all keys are used and are considered equivalent as base for DNSSEC
proofs.

Note that systemd-resolved will automatically use a built-in trust anchor key for the
Internet root domain if no positive trust anchors are defined for the root domain. In most
cases it is hence unnecessary to define an explicit key with trust anchor files. The built-in
key is disabled as soon as at least one trust anchor key for the root domain is defined in
trust anchor files.

It is generally recommended to encode trust anchors in DS resource records, rather than
DNSKEY resource records.

If a trust anchor specified via a DS record is found revoked it is automatically removed from
the trust anchor database for the runtime. See RFC 5011[5] for details about revoked trust
anchors. Note that systemd-resolved will not update its trust anchor database from DNS
servers automatically. Instead, it is recommended to update the resolver software or update
the new trust anchor via adding in new trust anchor files.

The current DNSSEC trust anchor for the Internet's root domain is available at the IANA Trust
Anchor and Keys[6] page.

NEGATIVE TRUST ANCHORS
Negative trust anchors define domains where DNSSEC validation shall be turned off. Negative
trust anchor files are found at the same location as positive trust anchor files, and follow
the same overriding rules. They are text files with the .negative suffix. Empty lines and
lines whose first character is ";" are ignored. Each line specifies one domain name which is
the root of a DNS subtree where validation shall be disabled. For example:

# Reverse IPv4 mappings
10.in-addr.arpa
16.172.in-addr.arpa
168.192.in-addr.arpa
...
# Some custom domains
prod
stag

Negative trust anchors are useful to support private DNS subtrees that are not referenced
from the Internet DNS hierarchy, and not signed.

RFC 7646[7] for details on negative trust anchors.

If no negative trust anchor files are configured a built-in set of well-known private DNS
zone domains is used as negative trust anchors.

It is also possibly to define per-interface negative trust anchors using the
DNSSECNegativeTrustAnchors= setting in systemd.network(5) files.

SEE ALSO
systemd(1), systemd-resolved.service(8), resolved.conf(5), systemd.network(5)

NOTES
1. RFC 4035, Section 4.4
https://tools.ietf.org/html/rfc4035#section-4.4

2. RFC 1035, Section 5
https://tools.ietf.org/html/rfc1035#section-5

3. RFC 4034, Section 5
https://tools.ietf.org/html/rfc4034#section-5

4. RFC 4034, Section 2
https://tools.ietf.org/html/rfc4034#section-2

5. RFC 5011
https://tools.ietf.org/html/rfc5011

6. IANA Trust Anchor and Keys
https://data.iana.org/root-anchors/root-anchors.xml

7. RFC 7646
https://tools.ietf.org/html/rfc7646

systemd 249 DNSSEC-TRUST-ANCHORS.D(5)